The disclosure relates to a hydroelectric converter having the features of the disclosure, to a converter arrangement having a converter of this type, and to a method for actuating a converter of this type.
Converters of this type are used, for example, in wave power plants, as are described in U.S. Pat. No. 6,300,698. Said known wave power plant has a hydraulic cylinder which is operatively connected to a buoy, with the result that the hydraulic cylinder is actuated by the swell and the corresponding movement of the buoy and therefore, as pump, conveys pressure medium into a hydraulic circuit, with the result that a downstream hydraulic accumulator and a hydraulic machine can be charged and driven, respectively. An output shaft of said hydraulic machine is connected to a generator, with the result that the hydraulic energy is converted into electrical energy. Since the swell varies greatly both with regard to the wave height and the frequency, a complicated electronic circuit has to be provided in order to homogenize the generator output voltage.
DE 10 2007 018 600 A1 proposes an improved converter, in which the hydraulic machine is configured with an adjustable delivery/displacement volume and is operated with speed regulation, in order to homogenize said fluctuations in the wave movement which result in corresponding fluctuations of the tapped-off electrical power.
DE 10 2008 021 576 A1 by the applicant discloses a corresponding converter, in which the oscillating body (buoy) is assigned a braking device in order to avoid excessive mechanical loading, with the result that the oscillating body can be braked if a predefined acceleration, frequency or speed is exceeded.
DE 10 2007 056 400 discloses a converter, in which the hydraulic machine can be adjusted in such a way that the piston of the hydraulic cylinder which acts as pump is loaded with a predefined damping force and a predefined pressure difference. The hydraulic accumulator is also charged by the pump in this solution.
In the above-described prior art, the converter is part of a wave power plant, but the disclosure is in no way restricted to applications of this type. In principle, a converter of this type can also be used in other systems which are preferably driven by a natural force. For instance, the pump can also be driven via a wind turbine, a tidal range or the like.
The common problem of all the abovementioned converters is that, on account of the stated inhomogeneities of the wave movements or the wind which drives the wind power plant, the electrical power which can be tapped off at the generator correspondingly also fluctuates, with the result that a largely homogeneous power tap-off can be realized only with considerable complexity in terms of control technology.
A further problem of converters of this type which are configured with a hydraulic accumulator consists in that the charging of the hydraulic accumulator is possible only when the pressure which is generated by the pump is higher than the pressure in the hydraulic accumulator. In said systems, the maximum pressure of the hydraulic accumulator also limits the system pressure, with the result that a complete conversion of the energy which is stored in the driving medium (wave energy, wind energy, etc.) into electrical energy is not possible. This problem is reinforced further by the fact that, on account of the comparatively limited hydraulic accumulator pressure, hydraulic damping of the pump which is driven by the wave energy or the wind energy is possible only to a restricted extent.
In principle, there is also the possibility, instead of a converter which is configured with a hydraulic accumulator, to couple the pump which is driven by the wave energy or the wind energy directly to an adjustable hydraulic machine which for its part drives a generator, or to couple the generator directly to the oscillating body. A system of this type is known, for example, from the “Wave-Swing” project. It is disadvantageous in directly coupled systems of this type that the power tap-off likewise fluctuates depending on the fluctuations of the natural force (wave energy, wind energy, etc.) and flywheels or the like have to be used in order to store the energy in the event of an energy excess, which flywheels or the like in turn require a considerable amount of installation space and, moreover, increase the complexity in terms of device technology.
The kinetic energy which is tapped off via a PTO (power take-off device) of this type is in principle the product of a damping force on the movement of the PTO and the movement speed. In order to obtain an optimum power tap-off, the damping force and the movement speed have to be varied and reversed during the wave cycle, in order to carry out an optimum adaptation to the respective movement speed of the float or the like. Accordingly, in converters of this type, the damping force and the movement speed have to be regulated, in order to make the optimum power tap-off possible. In wave power plants, said power tap-off accordingly varies twice during each wave cycle between the maximum values at the wave peak and at the swell and the two zero crossings which lie between them.
In contrast, the disclosure is based on the object of providing a hydroelectric converter, a converter arrangement having a converter of this type, and a method for actuating a converter of this type, which make homogenized power tap-off possible even in the case of fluctuations in the input power or energy.